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    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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    <script>
      let z = 30;
      let n = prompt("number");
      // 参数 x,y === 局部变量x,y
      function fn(x = 100, y = 200) {
        console.log(x, y, x + y);
      }
      fn(z, 20);
      fn(+n);
    </script>
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</html>
